Introducing a profile such as a curve or bend to a solid surface material is generally carried out according to two techniques, the first being post forming and the second thermoforming. The former method relates to the use of heat applied locally to a solid surface material to enable a curve or bend to be introduced. After a localised area which may be a region at or near the edge of a sheet is heated it is then physically bent by a press or sandwich mould before it cools. Although this technique has met with some success when used with some solid surface materials, it has been found that when acrylics are bent in this way, serious problems occur in the material such as crazing, cracking, blanching and lowering of impact resistance. In the worse case, acrylic solid surface veneer material curved by post forming can simply break away in the region of the bend. This renders the finish in the material commercially unacceptable.
Thermoforming is a term generally applied to the process of heat forming solid surface materials whereby heat is fully distributed over the whole surface area of the material even though bending is to take place in a relatively localised area of the sheet. One example of this process is that embodied in the applicant's own U.S. Pat. No. 5,236,658 which relates to a process and apparatus for heat forming of materials which have a thickness within or near the range of 8-20 mm. This patent is directed to the heat formation of solid surface materials such as Corian generically referred to as methyl methacrylate. Solid surface materials are by nature brittle and do not behave well under bending stresses. They nevertheless have high impact resistance and are very durable in such applications as kitchen bench tops and wall claddings. It is desirable for solid surface materials to be applied and finished without joins and with smoothly radiused curves. The technique involved in bending Corian in the manner described in U.S. Pat. No. 5,236,658 provides these curves and eliminates joins but this patent is specifically directed to the bending of thick sheets of thickness close to or between the range 8 mm and 20 mm which range is regarded in the industry as thick. Up until now, the industry has experienced significant problems in bending thinner but brittle materials such as solid surface veneer (acrylic) material for the reasons indicated above with reference to post forming.
According to the prior art techniques, attempts were made to bend thin solid surface veneer material but these produced poor results. Post forming was tried followed by thermoforming.
In the latter method, the thin solid surface veneer was heated in an oven using heating elements spaced apart from the surface of the sheets but it cracked at the bends which were formed in the material subsequent to heating. The material also suffered from blanching and blistering rendering this method of forming solid surface veneer unacceptable, to find a method which would produce commercially acceptable product. Thus, up until now it was not thought possible to bend thin solid surface material free of the defects previously experienced.
The inventor found that instead of an oven, if heating platens were placed in contact with or a short distance from thin solid surface material and the material then heated according to a predetermined time temperature regime, solid surface veneer could be formed with curves of a given radius without the problems of cracking, blanching, blistering, and reduction in impact resistance. The optimum time/temperature relationships were arrived at after trials and experimentation.